如何从 c# 访问元素或节点到 xml 文件

我有这个 xml 文件：

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="CDASchemas'cda'Schemas'CCD.xsl"?>
<!-- The following sample document depicts a fictional character’s health summary. Any resemblance to a real person is coincidental. -->
<ClinicalDocument xmlns="urn:hl7-org:v3" xmlns:voc="urn:hl7-org:v3/voc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:hl7-org:v3 CDA.xsd">
    <!-- 
********************************************************
CDA Header
********************************************************
-->
    <typeId root="2.16.840.1.113883.1.3" extension="POCD_HD000040"/>
    <templateId root="2.16.840.1.113883.10.20.1"/> <!-- CCD v1.0 Templates Root -->
    <!-- 
********************************************************
CDA Body
********************************************************
-->
    <component>
        <structuredBody>
<!-- 
********************************************************
Problems section
********************************************************
-->
<component>
<section>
    <templateId root='2.16.840.1.113883.10.20.1.11'/> <!-- Problem section template -->
    <code code="11450-4" codeSystem="2.16.840.1.113883.6.1"/> 
    <title>Problems</title> 
    <text>
        <table border="1" width="100%">
            <thead>
                <tr><th>Condition</th><th>Effective Dates</th><th>Condition Status</th></tr>
            </thead>
            <tbody>
                <tr><td>Asthma</td><td>1950</td><td>Active</td></tr>
                <tr><td>Pneumonia</td><td>Jan 1997</td><td>Resolved</td></tr>
                <tr><td>"</td><td>Mar 1999</td><td>Resolved</td></tr>
                <tr><td>Myocardial Infarction</td><td>Jan 1997</td><td>Resolved</td></tr>           
            </tbody>
        </table>
    </text>
    <entry typeCode="DRIV">
        <act classCode="ACT" moodCode="EVN">
            <templateId root='2.16.840.1.113883.10.20.1.27'/> <!-- Problem act template -->
            <id root="6a2fa88d-4174-4909-aece-db44b60a3abb"/>
            <code nullFlavor="NA"/>
            <entryRelationship typeCode="SUBJ">
                <observation classCode="OBS" moodCode="EVN">
                    <templateId root='2.16.840.1.113883.10.20.1.28'/> <!-- Problem observation template -->
                    <id root="d11275e7-67ae-11db-bd13-0800200c9a66"/>
                    <code code="ASSERTION" codeSystem="2.16.840.1.113883.5.4"/>                 
                    <statusCode code="completed"/> 
                    <effectiveTime><low value="1950"/></effectiveTime>
                    <value xsi:type="CD" code="195967001" codeSystem="2.16.840.1.113883.6.96" displayName="Asthma"/>
                    <entryRelationship typeCode="REFR">
                        <observation classCode="OBS" moodCode="EVN">
                            <templateId root='2.16.840.1.113883.10.20.1.50'/> <!-- Problem status observation template -->
                            <code code="33999-4" codeSystem="2.16.840.1.113883.6.1" displayName="Status"/>
                            <statusCode code="completed"/>
                            <value xsi:type="CE" code="55561003" codeSystem="2.16.840.1.113883.6.96" displayName="Active"/>
                        </observation>
                    </entryRelationship>
                </observation>
            </entryRelationship>
        </act>  
    </entry>

</section>
</component>
<section>
    <templateId root="2.16.840.1.113883.10.20.1.10"/> <!-- Plan of Care section template -->
    <code code="18776-5" codeSystem="2.16.840.1.113883.6.1"/>
    <title>Plan</title>
        <text>
        <table border="1" width="100%">
            <thead>
            <tr><th>Planned Activity</th><th>Planned Date</th></tr>
            </thead>
            <tbody>
            <tr><td>Pulmonary function test</td><td>April 21, 2000</td></tr>
            </tbody>
        </table>
    </text> 
    <entry typeCode="DRIV">
        <observation classCode="OBS" moodCode="RQO">
            <templateId root="2.16.840.1.113883.10.20.1.25"/> <!-- Plan of Activity activity template -->
            <id root="9a6d1bac-17d3-4195-89a4-1121bc809b4a"/>
            <code code="23426006" codeSystem="2.16.840.1.113883.6.96" displayName="Pulmonary function test"/>
            <statusCode code="new"/>
            <effectiveTime><center value="20000421"/></effectiveTime>
        </observation>
    </entry>
</section>
</component>
</structuredBody>
</component>
</ClinicalDocument>

我想解析这个文件，我想访问它的某些元素。所以我构建了这段代码：

class Program
{
    static String _TEMPLATE_ID_PROBLEM = "2.16.840.1.113883.10.20.1.11";
    static String _xmlName = "D:''Copy michele.castriotta@eresult (3).it''Projects''[2015 A] Decipher PCP''02 - phase 1''cda ccd''HL7_CCD_final''SampleCCDDocument.xml";
    static void Main(string[] args)
    {
        var doc = XDocument.Load(_xmlName);
        XElement root = doc.Root;
        //DEVO CERCARE DI SELEZIONARE LA SEZIONE GIUSTA
        IEnumerable<XElement>lista= root.XPathSelectElements("component/structuredBody/component/section");
        foreach (XElement e in lista)
        {
        //to do
        }
    }
}

但是列表"Lista"每次都是空的。错误在哪里？